Recovering hydrocarbons from subterranean zones typically involves drilling wellbores.
Wellbores are made using surface-located drilling equipment which drives a drill string that eventually extends from the surface equipment to the formation or subterranean zone of interest. The drill string can extend thousands of feet or meters below the surface. The terminal end of the drill string includes a drill bit for drilling (or extending) the wellbore. Drilling fluid, usually in the form of a drilling “mud”, is typically pumped through the drill string. The drilling fluid cools and lubricates the drill bit and also carries cuttings back to the surface. Drilling fluid may also be used to help control bottom hole pressure to inhibit hydrocarbon influx from the formation into the wellbore and potential blow out at surface.
Bottom hole assembly (BHA) is the name given to the equipment at the terminal end of a drill string. In addition to a drill bit, a BHA may comprise elements such as: apparatus for steering the direction of the drilling (e.g. a steerable downhole mud motor or rotary steerable system); sensors for measuring properties of the surrounding geological formations (e.g. sensors for use in well logging); sensors for measuring downhole conditions as drilling progresses; one or more systems for telemetry of data to the surface; stabilizers; heavy weight drill collars; and the like. The BHA is typically advanced into the wellbore by a string of metallic tubulars (drill pipe).
A bottom hole assembly may also include a mud hammer. A mud hammer acts to disrupt the flow of drilling fluid through the drill string to create a “pulsed” flow of drilling fluid. The pulses are delivered through the drill bit and help to dislodge and clear away drill cuttings from the drill bit. This may increase the drilling penetration rate.
A mud hammer typically comprises a piston and a port or orifice. The piston is biased away from the orifice by a bias force provided by a spring or other mechanism. A flow of drilling fluid drives the piston in an axial direction to restrict drilling fluid flow through the port. The bias force then moves the piston to a position where flow through the port can resume. The flow of drilling fluid thereby drives a self-starting oscillation of the piston, thereby alternatively allowing and restricting the flow of drilling fluid through the port. The mud hammer is configured so that during normal drilling operations, the opposing forces of the spring and the flow of drilling fluid result in the piston oscillating against the orifice, thereby generating periodic pulses in the flow of drilling fluid.
Modern drilling systems may include any of a wide range of mechanical/electronic systems in the BHA or at other downhole locations. Such electronics systems may be packaged as part of a downhole probe. A downhole probe may comprise any active mechanical, electronic, and/or electromechanical system that operates downhole. A probe may provide any of a wide range of functions including, without limitation: data acquisition; measuring properties of the surrounding geological formations (e.g. well logging); measuring downhole conditions as drilling progresses; controlling downhole equipment; monitoring status of downhole equipment; directional drilling applications; measuring while drilling (MWD) applications; logging while drilling (LWD) applications; measuring properties of downhole fluids; and the like. A probe may comprise one or more systems for: telemetry of data to the surface; collecting data by way of sensors (e.g. sensors for use in well logging) that may include one or more of vibration sensors, magnetometers, inclinometers, accelerometers, nuclear particle detectors, electromagnetic detectors, acoustic detectors, and others; acquiring images; measuring fluid flow; determining directions; emitting signals, particles or fields for detection by other devices; interfacing to other downhole equipment; sampling downhole fluids; etc. A downhole probe is typically suspended in a bore of a drill string near the drill bit.
A downhole probe may communicate a wide range of information to the surface by telemetry. Telemetry information can be invaluable for efficient drilling operations. For example, telemetry information may be used by a drill rig crew to make decisions about controlling and steering the drill bit to optimize the drilling speed and trajectory based on numerous factors, including legal boundaries, locations of existing wells, formation properties, hydrocarbon size and location, etc. A crew may make intentional deviations from the planned path as necessary based on information gathered from downhole sensors and transmitted to the surface by telemetry during the drilling process. The ability to obtain and transmit reliable data from downhole locations allows for relatively more economical and more efficient drilling operations.
Downhole electronics are typically powered by a downhole battery. The capacity of the downhole battery may limit the nature and the duration of the electronics operations that are performed downhole.
There are several known telemetry techniques. These include transmitting information by generating vibrations in drilling fluid in the bore hole (e.g. acoustic telemetry or mud pulse (MP) telemetry) and transmitting information by way of electromagnetic signals that propagate at least in part through the earth (EM telemetry). Other telemetry techniques use hardwired drill pipe, fibre optic cable, or drill collar acoustic telemetry to carry data to the surface.
A mud pulser may be used to perform MP telemetry. A mud pulser typically comprises an electrically-controlled valve which can be opened and closed in a coded pattern to create pressure waves in drilling fluid within a drill string. These pressure waves may be detected by a detector (e.g. a pressure transducer) at the surface. The intensity and the frequency of the pressure waves may be used to encode data to be transmitted to the surface.
Examples of mud pulsers are rotating disc valve mud pulsers and poppet valve mud pulsers. In a rotating disc valve mud pulser, a motor rotates a restrictor relative to a fixed housing to either allow or restrict the flow of drilling fluid through the housing. In a poppet valve mud pulser, a valve is move axially against an orifice to permit or restrict the flow of drilling fluid through the orifice.
The inventors have recognized that there remains a need for effective alternative means for generating controlled pressure pulses in drilling fluid for MP telemetry, for generating pressure pulses in drilling fluid to dislodge and clear away drill cuttings from a drill bit, and for generating electricity to power downhole electronics.